title: Efficient near-UV emitters based on cationic bis-pincer iridium(III) carbene complexes.
abstract: We report on the photophysical studies of two cationic near-UV emitters based on bis-pincer Ir(III) carbene complexes: [Ir(nBu)(C(NHC)(Me)CC(NHC))2]X, where Ir(nBu)(C(NHC)(Me)CC(NHC)) is (4,6-dimethyl-1,3-phenylene-κC(2))bis(1-butylimidazol-2-ylidene) and X = I(-) or PF6(-)). The compounds are highly emitting in deaerated CH3CN solution with emission maxima at 384 and 406 nm, and photoluminescence quantum yields of 0.41 and 0.38, for [Ir(nBu)(C(NHC)(Me)CC(NHC))2]I and Ir(nBu)(C(NHC)(Me)CC(NHC))2]PF6, respectively. In order to gain deeper understandings into their structural and electronic features, as well as to ascertain the nature of the excited states involved into the electronic absorption processes, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have been performed on the ground and excited states of the closely related complex [Ir(Me)(C(NHC)(Me)CC(NHC))2](+). In the solid state, an emission at low energy is observed (λ(max) = 500 nm) for both complexes. However, the intensity of the emission at high energy versus the intensity of the new emission at low energy is dependent on the nature of counterions. The origin of this emission is not completely clear, but the experimental data point to the formation of trapping sites induced by aggregation processes involving the interaction between the cationic emitter and the counterion.
authors.affiliation: NRW Graduate School of Chemistry, University of Münster , D-48149 Münster, Germany.
authors.forename: Noviyan
authors.initials: N
authors.lastname: Darmawan
authors.forename: Cheng-Han
authors.initials: CH
authors.lastname: Yang
authors.forename: Matteo
authors.initials: M
authors.lastname: Mauro
authors.forename: Matthieu
authors.initials: M
authors.lastname: Raynal
authors.forename: Susanne
authors.initials: S
authors.lastname: Heun
authors.forename: Junyou
authors.initials: J
authors.lastname: Pan
authors.forename: Herwig
authors.initials: H
authors.lastname: Buchholz
authors.forename: Pierre
authors.initials: P
authors.lastname: Braunstein
authors.forename: Luisa
authors.initials: L
authors.lastname: De Cola
mesh_terms: D002412:Cations; D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D007495:Iridium / Q000737:chemistry*; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D014466:Ultraviolet Rays
chemical_list: D002412:Cations; D056831:Coordination Complexes; C030011:carbene; D007495:Iridium; D008697:Methane